Separation of nitriles



Patented Nov. 8, 1949 SEPARATION OF NITRILES Richard B. Bishop, Haddonfield, and William I.

Denton, Woodbury, N. J., assignors to Socony- Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application June 26, 1947, Serial No. 757,316

and tungsten oxide. Caldwell and Chapman, Se-

rial No. 641,640, filed January 16, 1946, now Patent No. 2,450,632 Caldwell and Chapman, Serial No. 643,742, filed January 26, 1946, now abandoned and Benton and Bishop, Serial No. 645,012, filed February 1, 1946, now Patent No. 2,450,637.

In accordance with the practices-described in the above applications, there result mixtures of mononitriles with hydrocarbons, and in some cases polynitriles are also present.

In following the practices described in the above applications, it is often advantageous to start with a mixture of hydrocarbons such, for example, as Sovasol-74. Sovasol-74 is a mixture of hydrocarbons about 60% to 70% of which are aromatic. The remainder are chiefly naphthenes. Sovasol-74 is a tradename of the Socony-Vacuum Oil Company, Incorporated for an aromatic solvent obtained from catalytic cracking operations, having a boiling range of 280-370 F., a specific gravity of about 0.8443 and a mixed aniline point of 79. The advantage of using such a material as Sovasol-74 instead of a pure aromatic hydrocarbon is that it is cheaper and the nature of the process, as described in the above applications, is such that the naphthenes are converted to aromatic hydrocarbons, thus, in effect, providing a charge which is essentially all aromatic, at a cost equivalent to that of a mixed charge.

There are several disadvantages to the use of a mixed charge: 1) Mixed nitriles are formed which must be separated; (2) the higher-boiling hydrocarbons in the charge boil at temperatures very close to that at which benzonitrile boils; and (8) under some conditions of reaction hydrocarbon polymers are formed which boil in the same range as aromatic nitriles. The boiling point of benzonitrile is 372 F.

Because of the similarity of boiling points of the compounds involved, distillation does not 3 Claims. (01. 260465) 2 oifer a satisfactory means of separation. It has now been discovered that by the use of an alcoholwater mixture, within the proper range of proportions, the nitriles can be separated from the hydrocarbons, and also from the polynitriles, by solvent extraction. For example, a mixture of aromatic mononitriles and aromatic hydrocarbons has been found to be completely soluble in absolute ethyl alcohol. However, when sufficient Water is added to give an ethyl alcohol-water mixture containing about -85 alcohol and 1520 water, by volume, the hydrocarbons become insoluble but the mononitriles do not. If additional water is added until the alcohol-water contains about 6065% alcohol to 35-40 water, the mononitriles also become insoluble. Thus, it is apparent that by the use of ethyl alcohol-water mixture containing alcohol, for example, the

mononitriles may be dissolved and thus separated from the hydrocarbons. Since polynitriles are insoluble in alcohol-water mixtures containing more than 5% water, by using an 85 to 15% alcohol-water mixture they may be separated from the mononitriles with the hydrocarbon and recovered in a subsequent step.

By theuse of a continuous multi-phase extractor, a very thorough separation can be effected with an ethyl alcohol-water mixture containing as little water as 5% or as much water as 40%, by volume. The most desirable proportion to use will depend on the particular nitrile-hydrocarbon mixture to be separated.

Although ethyl alcohol .is preferred for the practice of the process of this invention, other alcohols, such as methanol and isopropyl alcohol, may be used with highly satisfactory results, and still other solvents such as acetone, acetic acid and the like are within the somewhat broader scope of this invention.

Since the solubility of the various components of the mixture to be separated vary with diiferent solvents, the desirable proportion of water to solvent may be expected to be different with different solvents. Likewise, the use of different nitriles and different hydrocarbons will require some modification of the solvent. However, the proportion of water to solvent in each case can easily be selected so as to provide a water-solvent mixture having the desired selective solvent effect.

Further understanding of the details and advantages of this invention may be gained by a consideration of the following specific examples.

Example I A hydrocanbon-mtrile residue obtained by the Per Cent Refractive Nitrogen Index Density Product before extractionm" 2. l3 1. 483 0. 8602 Extract A 7. 11 l. 5142 0. 9328 Extract B 5. 01 1. 5010 0. 9088 Railinate 0. 71 1.4740 0. 84i8 The increase in nitrogen content, refractive index and density in the extracts clearly indicates a concentration of the nitriles therein. Itis apparent from the above data, that a continuous multi-stage extraction would accomplish a very complete separation of the nitriles from the hydrocarbons.

Example II Synthetic mixtures of hydrocarbons and paratolunitrile were prepared and subjected to similar extraction with methanol-water mixtures. The hydrocarbons were a mixture of 44% alkyl benzenes, 43% methyl and dimethyl naphthalenes, and small amounts of a mixture of parafflns and naphthenes, having a boiling range of 392-516" R, an API gravity of 24.4, and a flash point of 175 F. The percentage of nitrogen, and hence the percentage of nitriles in each of th two extracts showed a considerable increase over the percentage of nitrogen and hence the percentage of nitriles in the original material. In one test, the mixture used consisted of 80% of methanol and 20% of water, by volume, and in a second test the solvent consisted of 90% methanol and 10 of water, by volume. The results were as follows:

Ori inal Extract #1 Extract #2 5 8 gg ggfi Per Cent Per Cent Nitrogen Nitrogen Nitrogen Tests indicate that polynitriles, like hydrocarbons, become insoluble as water is added to the-solvent, and before enough water is added to make the mononitriles also insoluble. However, the proportion of water may be adjusted first to a point where the polynitriles are relativel insoluble and the hydrocarbons, as well as the mononitriles, are relatively soluble. When methyl alcohol is used as the extractant, no water is required to make the methy1 alcohol selectively dissolve the hydrocarbons and mononitriles and The resulting extracts and r-ameral phenomena is observable, but the specific proportions of water differ. By the use of a proportion of water just sufficient to make the polynitriles relatively insoluble and both the mononitriles and hydrocarbons soluble, both the mononitriles and hydrocarbons may be separated from the polynitriles, by either a single stage or multistage extraction.

By further increasing the water content of the solvent mixture, the mononitriles may be separated from the hydrocarbons, after performing the separation described in the paragraph just preceding, or the mononitriles may be separated from both the hydrocarbons and the polynitriles, as described earlier in the specification, and the polynitriles later separated from the hydrocarbons by adjusting the proportions of water and solvent so that the mixture will efiect the separation.

In accordance with this invention, any solvent may be used which will, when undiluted with water, dissolve hydrocarbons and nitriles, and which is also miscible with water. It has been found that any such solvent, when mixed with water, progressively loses its ability rto dissolve, first polynitriles, then hydrocarbons, and then mononitriles. With this knowledge it is relatively simple to proportion the solvent and water so as to obtain a mixture that will selectively dissolve and thereby separate the mononitriles from the hydrocarbons and polynitriles, the mononitriles and hydrocarbons from the polynitriles, the polynitriles from the hydrocarbons, if no mononitriles are present, or the mononitriles from the hydrocarbons if no polynitriles are present.

The extraction operation may be accomplished in any well known manner, either in a single stage batch process, a continuous single stage process, a continuous multi-stage process or in a tower-type extraction process, Many methods and many types of equipment are already available in the prior art for this purpose, and will not be described here.

Temperature will obviously have an effect upon the dissolving power of the solvent mixture and hence it is within the scope of this invention to use any desired temperature either above or below room temperature and to adjust the proportions of solvent and water so that they will have the desired selectiveness at the temperature used. The examples given above were conducted at room temperature.

What is claimed is:

1. A method of separating aromatic mononitriles from a mixture containin aromatic mononitriles, aromatic polynitriles and aromatic hydrocarbons, that comprises extracting the mixture with a solvent mixture containing water and an alcohol, said solvent mixture containing a proportion of water to alcohol such that the solvent mixture will selectively dissolve the hydrocarbons and mononitriles in preference to the polynitriles, and thereafter extracting the resultant mixture of hydrocarbons and mononitriles with a solvent mixture containing water and an alcohol, said solvent mixture containing a larger proportion of water to alcohol such that the mixture will selectively dissolve the mononitriles in preference to the hydrocarbons.

2. A method of separating aromatic mononitriles from a mixture containing aromatic mononitriles, aromatic polynitriles and aromatic hydrocarbons, that comprises extracting the mixture with a solvent mixture containing water and ethyl alcohol, said solvent mixture containing a proportion of water to ethyl alcohol such that the solvent mixture will selectively dissolve the hydrocarbons and mononitriles in preference to the polynitriles, and thereafter extracting the resultant mixture of hydrocarbons and mononitriles with a solvent mixture containing Water and ethyl alcohol, said solvent mixture containing a larger proportion of water to ethyl alcohol such that the mixture will selectively dissolve the mononitriles in preference to the hydrocarbons.

3. A method of separating aromatic mononitriles from a mixture containing aromatic mononitriles, aromatic polynitriles and aromatic hydrocarbons, that comprises extracting the mixture with a solvent mixture containing water and ethyl alcohol, said solvent mixture containing a proportion of water to ethyl alcohol such that the solvent mixture will selectively dissolve the hydrocarbons and mononitriles in preference REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,133,007 Ralston et a1. Oct. 11, 1938 OTHER REFERENCES MacArdle, Solvents in Synthetic Organic Chemistry, (Van Nostrand), pp. 4750 (1925). 

